[ty] Improve diagnostics if the user attempts to import a stdlib module that does not exist on their configured Python version (#18403)

crates/ty_python_semantic/resources/mdtest/import/basic.md

@@ -176,3 +176,32 @@ emitted for the `import from` statement:
 # error: [unresolved-import]
 from does_not_exist import foo, bar, baz
 ```
+
+## Attempting to import a stdlib module that's not yet been added
+
+<!-- snapshot-diagnostics -->
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+import tomllib  # error: [unresolved-import]
+from string.templatelib import Template  # error: [unresolved-import]
+from importlib.resources import abc  # error: [unresolved-import]
+```
+
+## Attempting to import a stdlib module that was previously removed
+
+<!-- snapshot-diagnostics -->
+
+```toml
+[environment]
+python-version = "3.13"
+```
+
+```py
+import aifc  # error: [unresolved-import]
+from distutils import sysconfig  # error: [unresolved-import]
+```